Another source of valuable troubleshooting information is PostgreSQL itself. There are numerous views, tables, and functions dedicated to tracking and reporting various statistics and operating statuses for each hosted database. Principal among these is the
This view tells us what every database client is doing, where it is connected from, which user account it is operating under, and other important values. When administering a highly-available database, we must either have iron control over what executes in the database or the ability to quickly and easily assess its execution state. Besides using this data to track suspicious activity, we can also cancel long-running queries or Cartesian Products, or simply examine the connection turnover.
We probably use this view into the database more than any other, and it forms the backbone of several monitoring utilities as well. Let's explore just why this system catalog is so indispensable...